8mm will be a bit low lowered on planets, and overly high powered when barlowed IMO.
Assuming your dob has a focal length of 1200mm , you should aim for a 12mm eyepiece to give around 100x native which is good for dso's, and 200x for planets and the moon.
Maybe a 13mm Stratus or Hyperion would be the go.
Edit: Steve just beat me to it
